Phagocytosis is when a cell encloses a particle completely to form a phagosome. The process was originally evolved for the acquisition of nutrients by certain specialised cells. In multicellular animals, the process has been adapted to form a part of the immune system. Here, debris and pathogens are ingested by a macrophage, which then fuses with a lysosome to form a phagolysosome. Here, enzymes and toxic peroxides digest the pathogen.